GREEN, A.K.; SKOPEC, M.M.; KARASOV, W.H.; Univ. of Wisconsin, Madison; Univ. of Wisconsin, Madison; Univ. of Wisconsin, Madison: Flavonoids decrease 3-0-methyl D-glucose absorption in American robins
It is known that a variety of flavonoids inhibit glucose transport in vitro, including phloridzin and phloretin the potent inhibitors of intestinal sugar transporters SGLT1 and GLUT2. It is not known, however, whether commonly consumed flavonoids inhibit glucose absorption in wild frugivores. We tested for such an effect in American robins (Turdus migratorius) that depend almost entirely on fruit during a large portion of the year. We used a commonly consumed flavonoid with known in vitro inhibitory activity, quercetin and its 3-&beta-glycoside isoquercetrin. Using a pharmacokinetic approach involving serial blood collection and area under the curve calculations we determined if the flavonoids decreased the fractional absorption (FA) of 3-0-methyl D-glucose, the actively transported but non-metabolizable analogue of D-glucose. Food restricted robins were orally dosed with solutions containing 10mM D-glucose, 14C 3-0-methyl D-glucose with or without 10mM flavonoid. Robins were also injected IM with 14C 3-0-methyl D-glucose in saline iso-osmotic with avian blood. Compared to vehicle control, quercetin decreased the FA in 3 of 4 robins (range: -13.1 to + 2.5%), and isoquercetrin decreased FA in all 4 robins (range: -4.7 to �33.0%). Phloridzin decreased FA to a greater extent than either quercetin or isoquercetrin (range: -19.9 to �28.0%). It appears that some common plant secondary metabolites can decrease glucose absorption in a frugivorous bird. Supported by USDA (Hatch) WISO4322 NSF IBN-9723793 IBN-0216709
